This invention provides for a photographic element having a tough, stain resistant and transparent viewing surface and a stain resistant back side which is permeable to processing solutions. In particular, the present invention results in a photographic print that is viewed through a transparent support that protects against scratches and stains. On the side of the photographic element opposite to the transparent support is a processing-solution-permeable overcoat that becomes water resistant in the photochemically processed product. In one embodiment, a separate white or diffuse layer between the overcoat and the imaging layers provides a suitable background for the image.
Silver halide photographic elements contain light sensitive silver halide in a hydrophilic emulsion. An image is formed in the element by exposing the silver halide to light, or to other actinic radiation, and developing the exposed silver halide to reduce it to elemental silver.
In color photographic elements, a dye image is formed as a consequence of silver halide development by one of several different processes. The most common is to allow a by-product of silver halide development, oxidized silver halide developing agent, to react with a dye forming compound called a coupler. The silver and unreacted silver halide are then removed from the photographic element, leaving a dye image.
In either case, formation of the image commonly involves liquid processing with aqueous solutions that must penetrate the surface of the element to come into contact with silver halide and coupler. Thus, gelatin or similar natural or synthetic hydrophilic polymers have proven to be the binders of choice for silver halide photographic elements. Unfortunately, when gelatin or similar polymers are formulated so as to facilitate contact between the silver halide crystals and aqueous processing solutions, the resultant coatings are not as fingerprint and stain resistant as would be desirable, particularly in view of the handling or environment that an imaged photographic element may commonly experience at various times and circumstances. Thus, fingerprints can permanently mark the imaged element. The imaged element can be easily stained by common household products, such as foods or beverages, for example, coffee spills.
There have been attempts over the years to provide protective layers for gelatin based photographic systems that will protect the images from damages by water or aqueous solutions. U.S. Pat. No. 2,173,480 describes a method of applying a colloidal suspension to moist film as the last step of photographic processing before drying. A series of patents describes methods of solvent coating a protective layer on the image after photographic processing is completed and are described in U.S. Pat. Nos. 2,259,009, 2,331,746, 2,798,004, 3,113,867, 3,190,197, 3,415,670 and 3,733,293. U.S. Pat. No. 5,376,434 describes a protective layer formed on a photographic print by coating and drying a latex on a gelatin-containing layer bearing an image.
Various lamination techniques are known and practiced in the trade. U.S. Pat. Nos. 3,397,980, 3,697,277 and 4,999,266 describe methods of laminating a polymeric sheet film, as a protective layer, on a processed image.
Protective coatings that need to be applied to the image after it is formed, whether by coating or by lamination, several of which were mentioned above, adds a significant cost to the final imaged product. The processing equipment needs to be modified and the personnel running the processing operation need to be trained to apply the protective coating. A number of patents have been directed to water-resistant protective coatings that can be applied to a photographic element prior to development. For example, U.S. Pat. No. 2,706,686 describes the formation of a lacquer finish for photographic emulsions, with the aim of providing water- and fingerprint-resistance by coating the light-sensitive layer, prior to exposure, with a porous layer that has a high degree of water permeability to the processing solutions. After processing, the lacquer layer is fused and coalesced into a continuous, impervious coating. More recently, U.S. Pat. No. 5,853,926 to Bohan et al. discloses a protective coating for a photographic element, involving the application of an aqueous coating comprising polymer particles and a soft polymer latex binder. This coating allows for appropriate diffusion of photographic processing solutions, and does not require a coating operation after exposure and processing. Again, however, the hydrophobic polymer particles must be fused to form a protective coating that is continuous and water-impermeable. U.S. Pat. No. 5,856,051 describes the use of hydrophobic particles with gelatin as the binder in an overcoat formulation. This invention demonstrated an aqueous coatable, water-resistant protective overcoat that can be incorporated into the photographic product, allows for appropriate diffusion of photographic processing solutions, and does not require a coating operation after exposure and processing. Again, however, fusing is required by the photofinishing laboratories to render the protective overcoat water-resistant.
Commonly assigned U.S. Ser. No. 09/235,436 discloses the use of a processing solution permeable overcoat that is composed of a urethane-vinyl copolymer having acid functionalities. Commonly assigned U.S. Ser. Nos. 09/235,437 and 09/448,213 disclose the use of a second polymer such as a gelatin or polyvinyl alcohol to improve processibility and reduce coating defects. Commonly assigned U.S. Ser. No. 09/621,267 discloses the use of a processing solution permeable overcoat that is composed of a various water dispersed polymers that will coalesce into a water-resistant protective overcoat at elevated temperature, following processing, without fusing.
Thus, polymeric latex overcoats have been coated to provide protection to the image side of a print while allowing photographic development of the imaging layers. These overcoat layers, however, often fail to provide complete or desired protection. Specifically, they are prone to some damage during processing.
In conventional photographic elements for the production of color images to be viewed by reflected light (xe2x80x9ccolor paperxe2x80x9d), opaque support layers are traditionally used, e.g., paper which may be been rendered hydrophobic on one or both sides by a coating with polymers such as polyethylene. The opaque support layer generally provides the pale, preferably white, light-reflective image background for the image to be produced for viewing by reflected light. In contrast, U.S. Pat. No. 4,355,099 to Trautweiler discloses an imaging layer comprising a transparent support, imaging layers and a gelatin based protective layer. The photographic layers are exposed and the resulting images viewed through a transparent support layer while the processing liquids required for development enter the photographic layers from the active, coated side, and the imaging element is bonded to a main support after processing. To facilitate bonding of the material (the protective layer) to the main support, the transparent layer support is a thin auxiliary support not more than 50 xcexcm in thickness. In one particular embodiment, a reflection layer may be placed above the photographic layers so that the image produced may be independent of the reflection characteristics of the main support. The photographic element of Trautweiler avoids some of the disadvantages of traditional gelatin overcoats, namely susceptibility to water and stain damage, mentioned above. One disadvantage of Trautweiler""s imaging element is that the method employed for its processing necessarily includes bonding of the material to the main support, which is very cumbersome.
U.S. Pat. No. 4,480,027 to Schon et al. discloses an imaging element that has a transparent support, imaging layers and a reflective layer, in that order. The reflective layer has to be permeable to alkaline developing solutions. Although, it is not mandatory, the patent discloses that the reflective layer can be comprised of gelatin as the binder. Schon et al. conducted a stain test on the image side of the imaging element, which in this case is protected by the transparent support. Schon et al. did not perform a stain test on the reflective layer side.
The patents to Schon et al. and Trautweiler do not teach an imaging element that is processable and then stain resistant on both sides, unless lamination is done.
Imaging elements have been overcoated with polymeric latex overcoats to provide protection to the image side of a print while allowing photographic development of the imaging layers. However, these overcoats are prone to some damage during processing, which can result in an objectionable appearance. Any scratches in the overcoat will be visible and may prevent the overcoat from protecting the image against stain or water resistance.
This invention provides for a photographic element having a tough, stain resistant and transparent viewing surface and a stain resistant backside which is permeable to processing solutions. The resulting photographic print is viewed through a transparent support that provides protection against scratches and stains. On the side of the photographic element opposite to the transparent support is a processing-solution-permeable protective coating that becomes water resistant in the photochemically processed product. The formulation for the protective coating comprises at least one water-dispersible polymer (or latex) interspersed with a water-soluble polymer. During development or thereafter, before drying, the water-soluble polymer is removed to a significant extent, facilitating coalescence of the residual water-dispersible polymer, thereby forming a water-resistant and stain-resistant continuous protective overcoat. Either the protective layer can provide an opaque background for the image, and/or a white or diffuse layer between the polymeric coating and the imaging layers can also be provided.
The polymeric coating provides water and stain protection to the reverse of the print where minor scratches or damage is not critical since the image is not viewed from this side. The transparent support which forms the viewing surface is tough, stain-proof, and can be wiped clean without potential damage. The back of the print is also rendered stain proof after the processing is completed. Minor blemishes that are intrinsic to these type of polymer films will not affect image quality, while maintaining print durability.
Another aspect of the invention provides for a method of forming an image in the imaging element described above and converting the overcoat into a water-resistant coating.